High speed printer with gas-operated sheet feeding

ABSTRACT

A high speed printer for printing on sheets of porous media supplied from a stack of such sheets includes opposed pagewidth printheads. A sheet pick-up assembly is positioned operatively upstream of the pagewidth printheads. The sheet pick-up assembly has a gas conduit in fluid communication with a reversible gas supply, an outlet of the gas conduit being oriented so that the outlet is directed towards a top sheet of the stack such that a stream of gas can be directed out of the outlet and onto the top sheet to penetrate the top sheet and generate a cushion of gas between the first sheet and a second sheet to separate the first and second sheets. The reversible gas supply reverses the direction of the stream of gas back into the outlet to draw the first sheet against the outlet. A sheet feed mechanism is operatively arranged with respect to the, or each printhead and has a displacement mechanism for displacing the gas conduit to feed the first sheet from the stack.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.10/982,785 filed on Nov. 8, 2004, which is a continuation of U.S.application Ser. No. 10/713,082 filed on Nov. 17, 2003, now issued asU.S. Pat. No. 6,830,246, which is a continuation of U.S. applicationSer. No. 10/309,230 filed on Dec. 4, 2002, now issued as U.S. Pat. No.6,659,447, which is a continuation of U.S. application Ser. No.10/052,425 filed on Jan. 23, 2002, now issued as U.S. Pat. No.6,619,654, the entire contents of which are herein incorporated byreference.

FIELD OF THE INVENTION

This invention relates to an apparatus for feeding sheets of media froma stack of the media. In particular, this invention relates to anapparatus for feeding porous sheets of a media from a stack of suchsheets.

BACKGROUND TO THE INVENTION

The applicant has developed various printheads which provide high speed,photographic quality printing. The printheads comprise ink jet nozzlesarranged in an array. The ink jet nozzles are formed usingmicroelectromechanical systems (MEMS) technology. The use of MEMStechnology results in very high speed printing capabilities where pagescan be printed at a rate of up to two pages per second (for double-sidedprinting).

To facilitate such high speed printing, it is important, firstly, thatthe paper fed to the printing station of the printer is accuratelyaligned and capable of the required feed rate with as little likelihoodas possible of paper jams or the like, occurring. Secondly, the papermust be able to be fed to the printing station at a rate sufficient touse the high speed printing capabilities of the printing station to itsfullest extent.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided anapparatus for feeding porous sheets of media from a stack of suchsheets, the apparatus comprising

a support structure for supporting the stack;

a gas conduit that is mounted on the support structure and has an outletthat is oriented so that, when the stack is positioned on the supportstructure, the outlet is directed towards a first sheet of the stack,the gas conduit being in fluid communication with a gas supply so that astream of gas can be directed onto the first sheet to penetrate thefirst sheet and generate a cushion of gas between the first sheet and asecond sheet to separate the first and second sheets; and

a sheet feed mechanism arranged on the support structure for feeding thefirst sheet from the stack once the first and second sheets areseparated.

The sheet feed mechanism may include a displacement mechanism fordisplacing the gas conduit relative to the support structure, the gassupply being reversible to draw the first sheet against the outlet oncethe first sheet has separated from the stack.

The conduit may include a fluid hose and a pick-up bar connected to thefluid hose, the outlet being an aperture defined in the bar, which isdimensioned to span the stack of sheets.

The displacement mechanism may include a roller assembly that is mountedon the support structure downstream of the pick up bar to receive thefirst sheet from the pick up bar.

The pick-up bar may have a foot portion of increased transverse profileso that a region of low pressure is generated between the first sheetand the foot portion to aid separation of the first sheet from thestack.

The displacement mechanism may include an axle that is rotatably mountedwith respect to the support structure, a motor that is connected to theaxle for rotatably driving the axle and at least one arm that isconnected to an end of the axle. The pick-up bar may be pivotallymounted on the, or each, arm, so that, on rotation of the axle, thepick-bar is displaced with respect to the support structure.

According to a second aspect of the invention, there is provided anapparatus for feeding porous sheets of media from a stack of suchsheets, the apparatus comprising

A retaining structure that is configured to retain the stack in analigned condition;

A pick-up device that is operatively arranged with respect to theretaining structure, the pick-up device including a gas conduit that isin fluid communication with a gas supply and a nozzle arrangement thatis in fluid communication with the gas conduit, the nozzle arrangementbeing shaped to define a pick-up surface, the pick-up device beingdisplaceable along a feed path relative to the retaining structure, thepick-up device being positioned so that the nozzle arrangement iscapable of directing a flow of gas onto a first sheet of the stack suchthat the gas passes partially through the first sheet and impinges on asecond sheet, generating a cushion of air between the first and secondsheets to separate the first and second sheets, the gas supply beingreversible so that the first sheet can be drawn towards the pick-upsurface and retained against the pick-up surface; and

A displacement mechanism that is operatively arranged with respect tothe retaining structure for displacing the pick-up device along the feedpath so that the first sheet is fed from the stack along the feed path.

The nozzle arrangement may be shaped so that, as the gas flow is appliedto the first sheet at a suitable rate, a region of relatively lowpressure is generated between the pick-up surface and the first sheetthereby to facilitate displacement of the first sheet towards thepick-up surface.

The apparatus may include a feed mechanism that is operativelypositioned with respect to the retaining structure, downstream of thepick-up device for receiving the first sheet from the pick-up device.

The feed mechanism may be in the form of a roller assembly.

The pick-up device may include a pick-up bar that spans the stack ofmedia, the nozzle arrangement being mounted on the pick-up bar and thegas conduit being in the form of an air hose that is attached to thepick-up bar and is connected to the nozzle arrangement.

The displacement mechanism may include an axle that is rotatably mountedwith respect to the retaining structure. A motor may be connected to theaxle for rotatably driving the axle. At least one arm may be connectedto an end of the axle, the pick-up bar being pivotally mounted on the,or each, arm, so that, on rotation of the axle, the pick-bar isdisplaced along the feed path.

According to a third aspect of the invention, there is provided a methodof separating a sheet of print media from a stack of sheets, the sheetsbeing porous and the method including the steps of:

blowing fluid onto a top surface of a topmost sheet of the print mediaon the stack so that the fluid passes through at least the topmost sheetof the stack; and

capturing at least a part of the topmost sheet for conveyance to aprinting station of a printer.

The method may include blowing the fluid on to the top surface of thetopmost sheet through an aperture means of a pick-up means of a printmedia feed arrangement. The pick-up means may be in the form of apick-up bar. The aperture means of the pick-up bar may be in any of anumber of different forms. For example, the aperture means may be in theform of a channel extending longitudinally along the bar. Instead, thebar may support a plurality of longitudinally spaced, discrete orifices,the orifices defining the aperture means.

The method may include, initially, prior to capturing said at least partof the topmost sheet, lifting said at least part of the topmost sheetfrom the stack. The method may include causing said lifting of said atleast a part of the topmost sheet by creating a low pressure regionbetween a face of the pick-up means and the top surface of the topmostsheet of print media.

According to a fourth aspect of the present invention there is provideda method of separating a sheet of print media from a stack of sheets,the sheets being porous and the method includes the steps of:

applying high pressure to a fluid to cause said fluid to pass through atopmost sheet of the print media on the stack thereby separating thetopmost sheet from the stack; and applying low pressure to the fluid tolift from the stack a part of the topmost sheet.

Preferably, the method includes maintaining the pick-up means in spacedrelationship relative to the top surface of the topmost sheet of printmedia to cause said low-pressure region.

The method may include capturing said at least part of the topmost sheetof print media by the pick-up means, preferably by reversing a directionof fluid flow through the pick-up means to cause a change from a blowingaction to a suction action.

The method may include conveying said topmost sheet of print media in adirection substantially normal to a direction of flow of fluid blown onto the stack.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described by way of example with reference to theaccompanying drawings in which:

FIG. 1 shows a part of a printer including a print media feedarrangement operated in accordance with the method of the invention;

FIG. 2 shows a three-dimensional view of an input region of the printerincluding part of the print media feed arrangement;

FIG. 3 shows a three dimensional view, on an enlarged scale, of the partof the print media feed arrangement of FIG. 2;

FIG. 4 shows a schematic, sectional side view of an initial stage ofoperation of the print media feed arrangement;

FIG. 5 shows a schematic, sectional side view of a second stage ofoperation of the print media feed arrangement;

FIG. 6 shows a schematic, sectional side view of a third stage ofoperation of the print media feed arrangement; and

FIG. 7 shows a schematic, sectional side view of a fourth stage ofoperation of the print media feed arrangement.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring initially to FIG. 1 of the drawings, a part of a printer isillustrated and is designated generally by the reference numeral 10. Theprinter 10 is a high speed printer which prints both sides of printmedia at the rate of approximately one sheet per second or two pages persecond (i.e. both sides of the sheet). The print media is, in this case,in the form of a stack of sheets. For ease of explanation, the inventionwill be described with reference to the print media being a stack of A4sheets of paper and, more particularly, sheets of paper having apredetermined degree of porosity.

The printer 10 uses a pair of opposed page width printheads 12, arrangedat a printing station 13, to print on both sides of sheets of paper fedthrough the printing station 13. Each printhead 12 is in the form of amicroelectromechanical systems (MEMS) chip having an array of ink jetnozzles to achieve the high speed, photographic quality printingdesired.

The printing station 13 includes a set of primary rollers 14, comprisinga drive roller 16 and a driven roller 18, arranged upstream of theprintheads 12 to convey a sheet of paper to the printheads 12. Asecondary set of rollers 20, comprising a first roller 22 and a secondroller 24, is arranged intermediate the printheads 12 and the set ofprimary rollers 14. A paper deflector 26 is arranged between the sets ofrollers 14 and 20.

As illustrated more clearly in FIG. 2 of the drawings, the print mediais, as described above, arranged in a stack 28. The stack 28 is receivedin a bin (not shown) of the printer 10 and is retained against a metalbulkhead 30 of the printer 10 in a suitable cabinet (also not shown). Atapping mechanism 32, which is solenoid driven, taps the paper stack 28to ensure that the sheets of the paper stack 28 are maintained inaccurate abutment with the metal bulkhead 30 so that, when a sheet isfed is to the printing station 13, as will be described in greaterdetail below, the sheet lifted from the stack 28 is aligned to be inregister with the printheads 12. In other words, the tapping mechanism32 inhibits skewing of a sheet picked from the stack 28.

The printer 10 includes a paper feed arrangement 34 for feeding a sheetof paper from the stack 28 to the rollers 16 and 18 of the set ofprimary rollers 14 so that the sheet of paper can be transported to theprinting station 13 for printing.

The feed arrangement 34 comprises a pivot rod or axle 36 which isrotatably driven by a drive means in the form of a stepper motor 38. Aswing arm 40 is arranged at each end of the axle 36.

The paper feed arrangement 34 includes a pick-up bar 42 which isconnected to a fluid hose 44. The pick-up bar 42 is pivotally attachedto the swing arms 40. An arm 46, having a bifurcated end (not shown)projects from one end of the bar 42. The arm 46 is slidably received ina sleeve in the form of a pivot block 48. The arm 46 and, moreparticularly, its bifurcated end, cooperates with an optical sensor 50to determine when the pick-up bar 42 is in its home position, the homeposition of the pick-up bar 42 being shown, schematically, in FIG. 4 ofthe drawings.

As described above, the printer 10 is a high-speed printer which has acapacity to print at the rate of one sheet per second. To make use ofthis capability, it is important that the sheets of paper are fedindividually to the printing station 13 from the stack 28 in anaccurate, controlled manner. Consequently, it is necessary for thepick-up bar assembly 34 to separate a sheet to be transported to theprinting station 13 from the stack 28 accurately. To separate a topmostsheet 28.1 from the stack 28, the fluid hose 44 is connected to a fluidsource (not shown). Air is blown down the hose 44 in the direction ofarrow 52 as shown in FIG. 4 of the drawings. The air exits through anoutlet aperture 54 of the pick-up bar 42 as shown by the arrows 56. Theair is forced between a foot portion 58 of the pick-up bar 42 and thetopmost sheet 28.1 of the paper stack 28.

The invention is intended particularly for use with print media which isporous such as, for example, 80 gsm paper.

Due to the porosity of the paper, air is also driven through the topmostsheet 28.1 and impinges on a sheet of the stack 28 which is second fromthe top, as shown by arrow 60 in FIG. 5 of the drawings. This results inan initial separation of the topmost sheet 28.1 from the remainder ofthe sheets of the stack 28.

Also, as a result of localised low pressure occurring between aperiphery of the foot portion 58 of the pick-up bar 42 and the topmostsheet 28.1 of the stack 28, the topmost sheet 28.1 is attracted to thepick-up bar 42 as shown in FIG. 6 of the drawings. Due to the passage ofair through the topmost sheet 28.1 separation of the topmost sheet 28.1from the remainder of the sheets of the paper stack 28 is aided.

Once the sheet 28.1 has been lifted off the stack 28 and transported ashort distance from the stack 28 and when the pick-up bar 42 reaches apredetermined altitude relative to the stack 28, the direction of flowof the air is reversed so that a suction effect is imparted at theaperture 54 of the pick-up bar 42. This is shown in FIG. 7 of thedrawings by arrows 62.

As the swing arms 40 of the paper feed arrangement 34 continue to rotatein the direction of arrow 64 (FIG. 3 of the drawings), the pick-up arm42 moves in the direction of arrow 66 (FIG. 7) so that a leading edge ofthe topmost sheet 28.1 of the paper stack 28 is fed between the rollers16 and 18 of the set of primary drive rollers 14. The suction is thenshut off in the hose 44 so that the sheet 28.1 is released from thepick-up bar 42 for onward conveyance by the sets of rollers 14 and 20 tothe printing station 13 for printing purposes.

It will be appreciated that the airflow parallel to a surface of thetopmost sheet 28.1 of the stack 28 results in a low friction cushionwhich facilitates translational motion of the sheet 28.1 relative to thepick-up bar 42. This allows the sheet 28.1 to be moved by any suitablemethod in a direction normal to a face of the pick-up bar 42 withouthindering the picking action of the pick-up bar 42. It also facilitatesmaintaining a trailing portion of the sheet 28.1 in spaced relationshiprelative to the stack 28 while the sheet 28.1 is being fed to the set ofrollers 14.

The applicant has found that the velocity of air through the fluid hosein the initial, “blowing” direction is not critical, nor is the spacingbetween the pick-up bar 42 and the topmost sheet 28.1 of the paper stack28. Further, the weight or grade of the paper of the stack is also notcritical provided that the paper in the stack has a degree of porosity.

Typically, a pressure of approximately 5 kPa is present in the fluidhose 14 when the air is blown on to the paper stack 28. The air isdelivered at approximately 1 l/s and exits the gap between the footportion 58 of the pick-up arm 42 and the topmost sheet 28.1 at apressure of approximately 1 kPa at a velocity of approximately 50 m/s.Experimentally, the pick-up arm 42 has been held at a spacing of between0.1 mm and 0.2 mm above the paper stack 28 to pick-up the topmost sheet28.1 and this has been found to be successful. In addition, the paperfeed arrangement 34 has been found to operate with paper of a grade from40 gsm to high resolution, photo-quality ink jet paper.

The aperture 54 of the pick-up bar 42 can also be any suitable shape.For example, the aperture 54 could be in the form of a straight or wavychannel extending the length of the pick-up bar 42. Instead, theaperture could comprise a plurality of discrete nozzles arranged atspaced intervals along the length of the pick-up bar 42.

The applicant has found that, surprisingly, by blowing air on to thepaper of the stack 28 separation of the sheets is facilitated. This isan entirely counter-intuitive approach, as one would expect that asuction-type mechanism would operate better. However, provided the paperof the stack 28 is porous, very good separation of the topmost sheet ofpaper from the stack 28 can be effected.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A high speed printer for printing on sheets of porous media suppliedfrom a stack of such sheets, the printer comprising at least onepagewidth printhead; a sheet pick-up assembly positioned operativelyupstream of the, or each, pagewidth printhead, the sheet pick-upassembly having a gas conduit in fluid communication with a reversiblegas supply, an outlet of the gas conduit being oriented so that theoutlet is directed towards a top sheet of the stack such that a streamof gas can be directed out of the outlet and onto the top sheet topenetrate the top sheet and generate a cushion of gas between the firstsheet and a second sheet to separate the first and second sheetswhereupon the reversible gas supply reverses the direction of the streamof gas back into the outlet to draw the first sheet against the outlet;and a sheet feed mechanism operatively arranged with respect to the, oreach printhead, the sheet feed mechanism having a displacement mechanismfor displacing the gas conduit to feed the first sheet from the stack.2. A high speed printer as claimed in claim 1, which includes a pair ofopposed pagewidth printheads for duplex printing.
 3. A high speedprinter as claimed in claim 2, in which the conduit includes a fluidhose and a pick-up bar connected to the fluid hose, the outlet being anaperture defined in the bar, which is dimensioned to span the stack ofsheets.
 4. A high speed printer as claimed in claim 3, in which thedisplacement mechanism includes a roller assembly that is operativelyarranged with respect to the pagewidth printheads downstream of the pickup bar to receive the top sheet from the pick up bar.
 5. A high speedprinter as claimed in claim 4, in which the roller assembly includes aset of primary rollers arranged upstream of the printheads to conveyeach sheet of print media to the printheads and a set of secondaryrollers positioned intermediate the primary rollers and the printheads.6. A high speed printer as claimed in claim 3, in which the pick-up barhas a foot portion of increased transverse profile so that a region oflow pressure is generated between the first sheet and the foot portionto aid separation of the first sheet from the stack.
 7. A high speedprinter as claimed in claim 3, in which the displacement mechanismincludes a rotatable axle, a motor that is connected to the axle forrotatably driving the axle and at least one arm that is connected to anend of the axle, the pick-up bar being pivotally mounted on the, oreach, arm, so that, on rotation of the axle, the pick-bar is displaced.